This invention relates to the fabrication of printed circuit boards.
In a standard printed circuit board manufacturing operation, a solder mask is applied to the board so as to expose areas of copper pads which are to be soldered. A flux is then applied to the board, followed by submerging the board in a molten solder bath. Upon removal of the board, blasts of hot air are used to remove excess solder. The boards are then cleaned to eliminate any contaminants.
The fluxes utilized in such processes are usually either rosin-based or water-soluble. Rosin-based fluxes are losing favor since, generally, they must be cleaned off by halogenated hydrocarbon solvents which are harmful to the environment. In terms of environmental protection, therefore, water-soluble fluxes are presently preferred. However, a major problem with most such fluxes is that they can significantly reduce the insulation resistance of the board as a result of flux residues absorbing moisture. They also tend to increase ionic contamination levels and exhibit poor copper coverage.
It is, therefore, an object of the invention to provide a method of fabricating printed circuit boards, including the step of applying a water-soluble solder flux thereto, which results in circuit boards having a high insulation resistance.
It is a further object to provide a water-soluble flux which does not significantly reduce the insulation resistance of boards to which it is applied and which exhibits good copper coverage and lower ionic contamination levels.